The present invention relates to an address data searching device for a data recording medium reproducing device.
According to one well known method of recording data on a video disc, recesses called "pits" are formed on the disc forming a coaxial or spiral track with data recorded by varying the lengths and/or spacings of the pits. Address data corresponding to the contents of recorded data is also recorded on the disc so that the contents of a desired record can be reproduced by supplying the appropriate address data. A pick-up device utilizing light is used to read the data of the disc. More specifically, a light beam applied to the disc is modulated by the presence or absence of pits on the disc as the beam passes through or is reflected by the disc with a data signal produced by demodulating the reflected or transmitted light.
In a data recording disc reproducing device for use with such a disc, the relative positions of the disc and the pick-up device must be finely adjusted. To this effect, the reproducing device is provided with a so-called tracking servo device which includes both a fine adjustment device and a coarse adjustment device. The fine adjustment device operates to control the rotation of a light deflecting tracking mirror so that the illuminating light beam correctly follows the data track on the disc at all times. The coarse adjustment device operates to coarsely adjust the relative positions of the disc and the pick-up device in the radial direction of the disc. More specifically, the coarse adjustment device drives, when address data has been supplied, a slider carrying the pick-up device and moves it in the radial direction of the disc so that the pick-up position is positioned on the track specified by the address data.
Heretofore, in such a reproducing device, when a desired address has been specified, the corresponding address on the disc is searched for with a technique in which address data read by the pick-up device is compared with the supplied address data and, according to a difference output between the supplied address and that corresponding to the current position of the pick-up device, the speed by which the slider is moved by the coarse adjustment device is controlled. However, this address data searching technique is disadvantageous in the following points. When drop-out occurs at a track position where the specified address data has been recorded because of damage to or fouling of the track, the control system does not operate satisfactorily as it then falls into a looping mode in which the searching operation around the position of the specified address data continues until the device is manually stopped. When the slider stops, it has a tendency to overshoot or go beyond the desired position due to inertia. Accordingly, in order to position the pick-up device on the track where the specified address data has been recorded, a complex stopping mechanism which provides compensation for overshooting of the slider must be provided for the slider driving section. Furthermore, since the slider moving speed is controlled according to the difference between the address data read by the pick-up device and the specified address data, the construction of a comparison circuit used for comparing the two data is necessarily intricate.
Accordingly, an object of the present invention is to provide an address data searching device in which the pick-up device is accurately positioned on the track where the desired address data has been recorded and, even if drop-out occurs on the track, the pick-up device will nevertheless still be stopped in the vicinity of the desired track.
Thus, a specific desired feature of the invention resides in that even in the case where the specified address data cannot be read because of the occurrence of drop-out, the pick-up device will still be positioned in the vicinity of the track where the specified address data is recorded.